The brain is critically dependent upon ambient blood glucose concentration for normal neuronal function. Although the interrelationship between blood glucose concentration and brain function has been recognized for years, few systematic studies of the impact of abnormal glucose levels on cognitive function are available. Diabetic populations have been most frequently studied because of their labile fluctuations in glucose in response to insulin injections and meal ingestion, with documented daily episodes of hypoglycemia alternating with transient or sustained hyperglycemia. Diabetes is also accompanied by multiple motor and sensory nerve lesions which cause functional impairments and can confound the clear differentiation between effects of metabolic derangements and those secondary to structural derangements. The proposed studies will assess diabetic subjects to evaluate neuropsychological functioning during a steady state of hypoglycemia (blood glucose = 50 mg/dl), euglycemia (blood glucose = 110 mg/dl) and hyperglycemia (blood glucose = 300 mg/dl) at glucose levels which frequently occur in insulin dependent diabetics. Blood glucose will be maintained by an insulin infusion system (Biostator), providing a method for precise regulation of blood glucose concentration during testing. The following questions will be assessed through the proposed studies: 1. To what extent is central brain processing, which may mediate visual perception and motor responding, impaired at altered glucose levels? 2. To what extent is central brain processing, which may mediate auditory perception and motor responding, impaired at altered glucose levels? 3. What is the relationship between higher inferential or associative brain processing required for reading comprehension and altered levels of blood glucose?